onem2m-simple-config:iplugin-cfg-key-del doesn`t work properly

When deleting non existing cfg-key using next request
Post
http://localhost:8181/restconf/operations/onem2m-simple-config:iplugin-cfg-key-del
{
"input":

{ "plugin-name": "Onem2mExample", "instance-name": "default", "cfg-key": "testKey2" }

}

it will pass first time even though it doesn`t exist and crash second time causing to crash other requests too ->
POST
http://localhost:8181/restconf/operations/onem2m-plugin-manager:onem2m-plugin-manager-simple-config-client-registrations

POST
http://localhost:8181/restconf/operations/onem2m-simple-config:iplugin-cfg-get-startup-config

POST
http://localhost:8181/restconf/operations/onem2m-simple-config:iplugin-cfg-get-running-config